Automatic gain control



Aug. 13, 1935 P. BORIAS Y 2,010,842

AUTOMATIC GAIN CONTROL Filed June 27, 1950 llllllll mun Hill

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INVENTOR PAUL 50R AS BY ATTORNEY Patented Aug. 13, 1935 AUTOMATIC GAIN CONTROL -Paul Borias, Paris, -France,.assignor .to QCom- .;pagnie Generale de Telegraphic SansFil, a cor- I Doration of France Application June 27, 1930, Serial- N0. 464,195 .In-France. June 29, 1929 1 Claim. (01. 250520) Y The present invention relates to improvements in amplifiers of oscillatory currents, for example those used in radio telegraphic and radio telephonic reception.

One of the main objects of the invention is to provide automatic regulation of the sensitivity of a receiver so as to maintain the intensity of reception at an appreciably constant level, in spite of variations of the energy received, for example anranti-fading device. v

Another object of the invention is to -provide decrease inthe reception intensity to any. suitable desired value, i. e., a device for the control of the sound volume.

Another important object of the invention is to provide a receiver wherein these twoeffects are easily, and-advantageously;combined by the action of, cooperating elements when being produced. i

Briefly, the construction upon which the invention is based, involves the combination of an indirectly heated tube-"used as detector tube, with a resistance which is to'produce a variable ohmic drop the resistance being interposed between the emitting cathode and the negative pole of the plate potential source. The other meansaccording to the invention, combined with the preceding ones, consists of amplifying elements with electronic emission elements; preceding the detector, the control electrodes of the elements being controlled inpotential by the potential drop in the above mentioned'resistance, and of devices for adjusting. thefeed' potential of the amplifying elements at will to a convenient and variable value.

' c Thenovel featureswhich I believe'to be characteristic of my invention areset forth in particularity in the appended claim, the invention itself, however, as to both its organization and methodkof operation will best be understood by reference to the following description taken in their output circuits, or anode circuits, all of which may be effected and arranged in any well connection with the drawing in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

In the drawing,

Fig. -1 diagrammatically showsan amplifying detecting device whose sensitiveness is automatically controlled in accordance with the invention,

Fig. 2 shows a device of the preceding type, means being added, in accordance with the invention, for theregulation of the feed potential of the electrodes of the amplifier which means may be utilized, if need be, as elementsfor the volume control.

of resistance 8.

Referring .to the accompanying drawing-in which like characters of reference indicate'the same parts in the different figures, an anti-fading receiver is shown in Fig. -1,the latter disclosing detectionlof the radio frequencyoscillations by means: of-a -multi-electrode tube termed an indirectly' ihea ted tube, i. e. provided with a cathode 2 heatedindirectly by a heating element 3. The anode-'4 of this tube 'is supplied by a source ofdirect currentpotential B, the positive terminal of the source'being connected,-by means of any suitable coupling device 5, with the utilization circuitfi, the latter being subsequent amplifi cation stages or even areproducer. For-the sakeof simplicity, the connections of the control electrode 1 of detector tube I ar'e not shown and they may be established in any of themanners knowniinthe priorart. The emitting cathode 2 "is connected to the negative terminal of thelanode source 13 across a resistance 8, the latter-being preferably shunt edby a capacity'fi. One, or more, amplifying tubes Ill, II are connected precedingdetecton- I, and are operatedin such a manner that the polarization potential of-their control electrodes is derived from the potential at the terminals Assuming, for example, that the cathodes of,

tubes l0 and H (which may be heated directly) are connected to thenegative terminal of source Band, .accordingly,'to one of theterminals of resistance 8, the return circuit of their control electrodes to the cathode will be joined-tothe otherend of resistance 8, as seen in Fig 1. An adjustable source 12, for the adjustment of the feed 'potentiaLmay optionally be inserted in this circuit. There are not shown, also for-the sakeof simplicity inorder to' facilitate the understandof'the invention, with respect to these tubes, the

heating circuit of their filament,"nor the input circuits o-r'elements of the control electrode, nor

known manner.

According to Fig. 2, the circuit arrangement of the type shown in Fig. 1 is modified so that the amplifier tubes and II have their grid potentials fixed by the connection of point I3, of their common filament heating circuit, to the slidable contact of a potentiometer resistance l4 shunting the anode source B. This arrangement is completed by the addition of a condenser [5 between the connecting wire l3, l4 and the negative terminalof the anode source. This circuit furnishes means, by the manipulation of the contact of potentiometer M, for adjusting the potential of rest of the grids of tubes l and of H, at will, to the suitable negative value'with respect to the cathodes of the same tubes. It is a matter of course that the heating circuit of the said cathodes must, on the other hand, be insulated.

In Fig.2 are indicated the connecting arrangements of the input-and output circuits of tubes it, H, l, the input circuit of tube It, the heating circuit of tube I. Thus, tubes Iii, II and l are excited by means of tuned radio frequency transformers T, T, T, and tube I6 by means of an audio frequency transformer T, the primary of the latter being shunted bycapacity IT. The assembly of the device is particularly well adapted to the construction of a receiver operating with frequency change, the tubes in and I l acting the part of amplifiers of currents of medium fre-. 7

quency, tube the one of second detector and tube i6, and possible following ones, that of am plifiers for low frequency currents. It is not thought necessary to show the details'of the connections of these latter tubes nor of-those of preceding tubeifi. It should be noted that the described arrangements furnish antifading amplifiers-detectors which may be fed entirely by the domestic light circuit, disposing of any use of batteries, equalization batteries or accumulators. and thereby represent new. indus trial products. To this end, the heating circuit of tubes l9 and l! is fed by the secondary A ofa transformer whose primary is branched off the supply line, the. latter notbeing shown. Another secondary A' grounded at M, feeds the heating circuit of detector i and, as thecase may be, of other tubes.

The operation of both Figs. 1 and 2 will now be described. In both Figs. 1 and 2 the detector is of the grid leak. type (as shown specifically in Fig. 2; at'9) and therefore has a decreased anode current fiow when the signal input increases. Hence, the drop acrossjresistor 8, in each figure, decreases when the signal input to the detector I rises above the desired volume level. L1 Fig. l, the battery i2 is employed for maintaining the grids of tubes M, H negative with respect to thecathodes thereof. beunderstood that between terminals a and a, andvb, b, are connected the tuned input circuits of the amplifier stages, as shown in detail in Fig. 2.

It will now-be seen that a rise of signal input to detector l'above a desired volume level results in a drop in anode current flow across resistorB. The point c of resistor 8 becomes less positive, and this results in the grids of tubes H3, H becoming more negative with respect to the cathodes thereof. The radio frequency amplification thereupon becomes less, and the sig nal input to detector ldecreases to the desired It is to.

I sistor i3, and lead H to the ground side of resistor H5. Hence, slider l4 (operating through lead 29) functions as a manual volume control by adjusting the cathode potential of each of tubes 98, ii. The resistor 8 functions, as in Fig. l, as a compensating resistor, and when the signal input to detector i rises above the desired volume level, the detector anode current drops.

There results a decreased drop across resistor 8, the point 0 becomes less positive, and the grids of tubes iii, H become less positively biased (or more negative therefore) with respect to the cathodes thereof. The, action is the same as described in connection with Fig. 1, and need not be repeated.

Finally, the anode source B will be established by means of one of the usual rectifying connecticns. It may prove. of advantage to make use of a single transformer with multiple secondaries for supplying the entire apparatus including the rectifier. Also that while I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications in the circuit arrangements, as well as in the apparatus employed, may be made without departing from the scope of my invention as set forth in the appended claim.

What I claim is:

, In a radio receiver, a radio frequency amplifier including an electron discharge tube, a detector of the grid leak type comprising an electron discharge tube provided with an electron emission electrode and a heating filament for said electrode, a source of potential for the anode of said detector tube, an impedance connected at one terminal thereof to the said emission electrode and the input circuit of said amplifier tube, the oppositeterminal being connected to the negative side of said source, a second impedance connected between the terminals of said potential source, said one terminal being connected to the signal input grid of the amplifier tube, and manual volume control means connected between'a point on the second impedance and the amplifier cathode in said amplifier input circuit.

' F PAUL BORIAS. 

